Time has come to harness nuclear power for water desalination

By LARRY C. WITTE

Published 9:55 pm, Friday, November 4, 2011

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Time has come to harness nuclear power for water desalination

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The spread of arid regions from prolonged drought in many parts of the world has been as fast as it has been remarkable. Severe water stress might become even more serious for the world's population than the need for energy.

Because water in many regions is being consumed faster than it's being replenished, potable water for human consumption or near-potable water for irrigation has become an increasingly scarce resource.

Water scarcity is now recognized as an issue of strategic importance. The U.S. government forecasts that at least 36 states will face water shortages within the next few years.

In Texas, we are now draining water at an alarming rate from underground reservoirs that have been there for thousands of years. The vast Ogallala aquifer, the primary water resource of the Great Plains, underlying 156,000 square miles, is seriously depleted. Extreme drought in recent years has made the situation worse, and forecasts show that water needs are expected to grow even as supplies may shrink because of increasing populations. The current drought might go on for another year, according to meteorologists, but even an end to the drought will not immediately replenish the vast underground aquifers.

Texas, of course, is not alone. Almost every part of the country is running into water problems. The expanding population of Arizona and Nevada is desperate for water. The water table of the highly productive San Joaquin Valley in California has been so lowered by intensive irrigation that the land has settled 30 feet in some places. Atlanta and its suburbs - home to 5 million people - came close a few years ago to seeing its principal water supply, Lake Lanier, dry up. There is talk that Atlanta's credit rating might even be downgraded because of its inability to cope with water issues.

Notably in Texas, El Paso, in conjunction with Fort Bliss, have developed a desalination plant to produce 27.5 million gallons per day (MGD) of fresh water using a previously unusable brackish ground water supply. It is said to be the largest inland desalination plant in the world.

Nuclear desalination is safe and reliable. The U.S. lags India and Japan in combining nuclear power with desalination. Currently eight nuclear reactors coupled to desalination units are operating in Japan. And plans to build nuclear desalination units are being considered in South America, Europe and the Middle East.

The technology for nuclear desalination is relatively simple. Energy from a reactor core is used to turn water into steam that passes through turbines to produce power. Some of the power can be used to drive pumps in a reverse osmosis filtration process that separates fresh water from salty seawater or brackish inland water sources. A flash distillation process can also be employed that uses the heat stored in the reactor coolant water directly.

What can be done to cope with this situation, especially in Texas?

Desalination could certainly be part of the solution. And since Texas needs power along with water, why not use nuclear reactors to provide energy and desalinated water simultaneously? The appeal of desalination is growing: between 2000 and 2005, desalination capacity increased by 41 percent worldwide.

A study funded by the Texas Water Development Board in 2006 showed that most desalination in Texas is for inland water sources rather than seawater. Currently desalination plants in the United States use oil or natural gas for fuel. But seawater desalination represents only 8 percent of installed capacity in the United States, compared to 60 percent worldwide.

The Texas Gulf Coast would be the right place for desalination reactors; they could take advantage of the availability of sea water for reactor cooling and desalination purposes. Risks like earthquakes, and earthquake-induced tsunamis, are very low in the Gulf of Mexico. It would make good sense to have a grid of pipelines eventually crisscrossing Texas, carrying not oil or natural gas, but fresh water

In fact, the National Research Council recently said that desalination of seawater and brackish groundwater "offers the potential to substantially reduce water scarcity … particularly in water-scarce regions, in localities experiencing rapid growth, or where users are able and willing to pay for high-quality, reliable new supply." A study by Argonne National Laboratory confirms that a nuclear plant that both generates electricity and provides heat for desalination would be more economical over its operating life than a similar plant using fossil fuels. And a nuclear plant doesn't emit greenhouse gases.

Protecting water resources is essential. State and local governments need to prevent excessive use of water. Recycling wastewater for irrigation can help. And rainwater can be recaptured through engineering to prevent excessive runoff, which would help replenish supplies. But such measures, however helpful and necessary, are not enough. Nuclear desalination plants could contribute substantially to our energy and water needs. The federal government could help address the water crisis by providing incentives for the development of dual-purpose reactors capable of providing electricity for commercial and residential use and heat for desalination.

If it seems difficult to foresee the use of nuclear desalination in Texas to provide relief from severe water shortages, it seems impossible to envisage our economy and environment remaining healthy for long without access to more fresh water. Today's water problems should be a warning of things to come.

Witte is a professor of mechanical engineering specializing in energy transport and thermodynamics at the University of Houston.